1. Technical Field
The present invention relates to a communication system, and in particular to a communication technique suitable for a mode in which a plurality of nodes perform communication via a common communication channel.
2. Related Art
In related arts, communication systems are known that have a plurality of nodes performing communication via a common communication channel. As such communication systems, JP-A-2009-296280 discloses a communication system with a configuration in which a plurality of nodes make a transition to a sleep state in order to reduce power consumption.
In this regard, for example, a controller area network (CAN) protocol defines two signal levels on a bus (communication channel), i.e., “dominant” and “recessive” levels. While in a state (bus idle state) where no bus signal is transmitted/received via the bus, the signal level on the bus is kept in keeps the recessive level. When a bus signal of the dominant level is transmitted from a node connected to the bus, the signal level on the bus becomes the “dominant” level.
The conventional CAN protocol (standardized in ISO 11898-5) defines that a node in a sleep state is woken up (i.e., turned into a wake-up state) when the bus signal of the dominant level is received from the bus. Therefore, in a communication system based on the conventional CAN protocol, when any bus signal is transmitted/received via the bus, all the nodes connected to the bus are turned into the wake-up state. In other words, all of the nodes connected to the bus are supposed to perform communication in the wake-up state. This raises a problem that the nodes which do not have to perform communication unnecessarily consume power.
As a measure against this problem, a recent CAN protocol (standardized in ISO 11898-6) defines a selective wake-up function for selectively waking up those nodes which are required to perform communication, among the nodes connected to the bus. The selective wake-up function realizes a partial network that enables communication in a state where a part of the nodes connected to the bus are woken up.
Specifically, a node in a sleep state may be configured to be woken up by receiving a wake-up frame that specifies its own node. However, such a configuration raises a problem that, when, for some reason, a node becomes unable to properly recognize the wake-up frame that specifies the own node, this node can no longer be woken up.